Methods of forming a protective film using PECVD while winding a continuous substrate with a long shape are known to be for example the following patent documents. Japanese Unexamined Patent Application Publication No. 11-350146 discloses a technique for forming a protective film, including applying power to a wire-mesh anode provided in a container, and converting a material gas passing through the anode into plasma, thus forming the protective film on the surface of a substrate of a magnetic recording medium in contact with an earthed cooling rotary drum. Japanese Unexamined Patent Application Publication No. 6-150310 discloses a technique for forming a protective film using radio frequency (RF) PECVD, including generating glow discharge between a pair of parallel flat-panel electrodes provided in a container, converting a material gas into plasma, and repetitively running continuous substrate between the electrodes, thus forming the protective film on the surface of a substrate of a magnetic recording medium. Japanese Unexamined Patent Application Publication No. 2000-336196 discloses a technique for forming an antireflective film using RF PECVD, including generating glow discharge between an electrode and a temperature control drum provided in a container, and converting a material gas into plasma, thus forming the antireflective film of titanium oxide on the surface of a polymer film in contact with the temperature control drum. Japanese Unexamined Patent Application. Publication No. 11-158637 discloses a technique for forming a protective film using microwave PECVD, including providing a reactor tube for radiating plasma in a container, feeding a base film on a can roll provided at a position facing the reactor tube, and forming the protective film on the surface of the base film of a magnetic recording medium.
However, in the method disclosed in Japanese Unexamined Patent Application Publication No. 11-350146, the means for converting the material gas into plasma is provided in an anode grid at a position facing the continuous substrate. Thus, because the material gas plasma is supplied to the continuous substrate at a position apart from the continuous substrate, the area where the film is simultaneously formed is limited. Hence, in order to form a film on the entire surface of the continuous substrate or to achieve an increase in the area where a film is formed, there is a need to prepare several anode grids, and undesirably the apparatus becomes complicated and expensive. Furthermore, because the material gas is supplied through the anode grids, deposits may be formed on the anode grids due to long-term film formation, undesirably deteriorating discharge stability.
Also in the method of forming a film using RF PECVD according to Japanese Unexamined Patent Application Publication No. 6-150310 and Japanese Unexamined Patent Application Publication No. 2000-336196, the film is formed even on the counter electrode. Upon long-term film formation, there may undesirably occur the generation of dust from the film deposited on the counter electrode or the changes in film-forming conditions attributed to changes in discharge impedance. In the method of forming a film using microwave PECVD according to Japanese Unexamined Patent Application Publication No. 11-158637, the means for converting the material gas into plasma is microwave introduced into the reactor tube provided at a position facing the continuous substrate. This method supplies the material gas plasma to the substrate at a position apart from the continuous substrate, and undesirably limits the area where a film is simultaneously formed and decreases the film formation rate. Furthermore, in order to form a film on the entire surface of the continuous substrate or to increase the area where a film is formed, several reactor tubes are required, and undesirably the apparatus becomes complicated and expensive.
Moreover in the conventional techniques disclosed in these patent documents, the resin of magnetic tape or antireflective film is used for the continuous substrate, and thus there is a need to reduce thermal load on the substrate at a film-forming temperature adjusted to about 150 degree Celsius or less. To this end, plasma cannot but be formed at a position apart from the substrate. Furthermore, because the resin-made continuous substrate has no conductivity, it cannot directly supply power to electrodes, making it impossible to form plasma along the surface of the substrate.
Also, methods of forming a film while winding a continuous substrate are known to be sputtering and deposition, in addition to PECVD. However, in any method of sputtering and deposition, a material gas is supplied from a target material or an evaporation source facing the substrate. So, the area able to simultaneously form a film is limited. Furthermore, properties of the formed film may undesirably vary depending on the distance from the supply source of material gas. Moreover, when using sputtering, the film formation rate is slower compared to when using PECVD. In the case of deposition, the evaporation source is a dot-type source, and an increase in the treatment area needs a plurality of evaporation sources, and undesirably the apparatus becomes complicated and expensive.